Complementary Metal Oxide Semiconductor (CMOS) image sensors generally offer advantages in the areas of integration, power consumption/dissipation and total system size in comparison to charge coupled device (CCD) image sensors. CMOS image sensors have come to dominate the image sensor marketplace for numerous applications, including, for example, camera phones, security cameras, PC video capture, bar-code scanners, fax machines, desk top scanners, toys, biometric devices and the like.
An image sensor, including CMOS image sensors, has “dark current.” Dark current is generally a signal level from an image sensor when the image sensor is not exposed to light, e.g., is in darkness. Dark current is analogous to a noise floor for an image sensor. In general, the lower the dark current, the better an image sensor performs, especially in low light conditions.
Some applications for image sensors, e.g., for military and/or satellite use, specify increased radiation hardness. For example, protons and gamma rays in the space environment can rapidly degrade an image sensor.